Anemia prior to or during COVID-19 is a risk factor for rehospitalization after SARS-CoV-2 clearance

Background: As the number of new and recovering COVID-19 cases continues to rise, it has become evident that patients can experience symptoms and complications after viral clearance. Clinical biomarkers characterizing patients who are likely to experience these prolonged effects are unknown. Methods: We conducted a retrospective study to compare longitudinal lab test measurements (hemoglobin, hematocrit, estimated glomerular filtration rate, serum creatinine, and blood urea nitrogen) in patients rehospitalized after PCR-confirmed SARS-CoV-2 clearance (n=49) versus patients not rehospitalized after viral clearance (n=173). Results: Compared to patients who were not rehospitalized after PCR-confirmed viral clearance, those who were rehospitalized had lower median hemoglobin levels in the year prior to COVID-19 diagnosis (cohens D = -0.74; p=0.01) and during the active infection window (cohens D = -1.02; p=2.4x10-7). Patients hospitalized after viral clearance were also more likely to be diagnosed with moderate or severe anemia during both intervals (pre-COVID: OR=5.91; p=0.03; active infection: OR=3.13; p=1.37x10-8). Conclusions: The diagnosis of moderate or severe anemia in the year prior to COVID-19 diagnosis and during active SARS-CoV-2 infection can aid in the identification of patients who are likely to be rehospitalized after viral clearance. Whether interventions to mitigate anemia in COVID-19 patients improve long term outcomes should be further investigated.